1. Field of the Invention
The invention relates in general to a spraying device which is mounted, or can be mounted, to the wrist axis of a robot or other multi-axis manipulator.
2. Description of the Related Art
In typical coating plants today, the possibly exchangeable atomizers mounted to robots or other program-controlled movable machines are connected to the necessary color changing and metering systems in the installation by external hoses. The color changers usually consist of modular valve assemblies, whose number corresponds to the selectable colors and which are combined in a block with a generally straight central passage common to all colors. The color chargers can, for example, be connected to a circulation line for the particular color (EP 0 979 964). Color changers of this type are also known which, to reduce space, contain a spiral groove in place of the usual straight central passage, at right angles to the longitudinal axis of the color changer manifold (DE 43 39 301), but this is less conducive to flow. In principle, color changers of this type enable a quick change between the available colors during paint operations. Although it is known that they should be located as close as possible to the paint application, in practice the color change valve arrangements have always been located outside the atomizer. For paint metering, volumetrically operating gear metering pumps or piston metering devices (metering cylinders) are used, which in newer systems are placed upstream or downstream of paint lines cleaned with a slug (DE 100 33 987, DE 101 57 966, DE 101 57 938, etc.). In their place, metering using closed-loop paint volume control is known, which basically consists of an electronic universal controller as the regulating device, a paint pressure regulator serving as an actuator and a flow rate meter for recording actual values, which are placed upstream of the main needle valve acting as the shut-off device in the customary atomizer (Dürr/Behr Technical Manual February 1994 “Paint Volume Control”; DE 101 42 355).
It is already known to install metering pumps configured as a gear pump or piston metering devices in the atomizer (DE 101 15 463; DE 101 36 720; EP 0693 319).
Because of the principle disadvantages of relatively long hose connections between the external color change valve arrangements and the atomizer, such as loss of paint or time, or cleaning problems when changing colors, the attempt has already been made to install color change systems in the atomizer, for example with several hollow needle valves permanently assigned to one color (WO 97/24189) or with several containers that can be pivoted around a common axis, which in one position are docked to the spray head and in another position to connections for an external color change valve arrangement (EP 0 792 695). These systems are relatively unwieldy and hardly practicable for small atomizers such as are needed for coating interiors, for example, or other confined work piece areas. Atomizers are further known with changeably mounted paint cartridges, which, for example, are emptied by a proportionally adjustable fluid drive located outside the atomizer on or in the paint robot (EP 0 967 016). Such systems have the principle disadvantage that time is lost in replacing the cartridge when changing colors.
A coating station was also proposed in DE 101 12 601 whose color changer, consisting in the usual way of paint valves, can be located in the atomizer. The atomizer here is intended to contain a metering valve constituting the primary needle valve of the atomizer to act as a controlled actuator for the rate at which the coating material emerges. The metering valve substitutes for a metering pump or other volumetrically operating metering device.
Generally, considerable disadvantages can be identified in the customary coating equipment using atomizers of the category considered here, such as color change losses caused by the components, relatively long color change times, high push losses when changing colors, in the case of paint volume control, low reaction times compared to a metering pump, high cost of installation and maintenance and/or other problems resulting from the spatial separation in the arrangement of the color change and metering devices.
An object of the invention is to avoid the disadvantages of the known systems and to propose a spraying device of the category considered that allows the least possible loss during color changes and at the same time shorter color change times. Preferably this should be achieved while requiring small amounts of space.